diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
index 0c3f915039..7f235fedef 100644
--- a/lib/matplotlib/colorbar.py
+++ b/lib/matplotlib/colorbar.py
@@ -487,7 +487,7 @@ class Colorbar:
             self.locator = ticks    # Handle default in _ticker()
 
         if isinstance(format, str):
-            self.formatter = ticker.FormatStrFormatter(format)
+            self.formatter = ticker.StrMethodFormatter('{:.3f}')
         else:
             self.formatter = format  # Assume it is a Formatter or None
         self.draw_all()
